This study is the largest prospective assessment of multiple markers of smoking status, duration, and intensity in relation to the risk of psoriasis. Using data from the Nurses Health Study II (NHS II), an ongoing longitudinal study of 116,608 female registered nurses from 15 states between the ages of 25 and 42 years at baseline who completed and returned an initial questionnaire in 1989, the researchers documented 887 incident cases of psoriasis during the 14 years of follow-up. Lifetime smoking exposure was measured in pack-years, equal to smoking 20 cigarettes per day for one year.

Compared with women who never smoked, the risk of psoriasis was 37 percent higher among past smokers and 78 percent higher among current smokers. Pack-years were associated with a graded increase in the risk for psoriasis. Compared with never smokers; the risk was 20 percent higher for one to ten pack-years, 60 percent higher for eleven to 20 pack-years, and more than two times higher for 21 pack-years.

The significant trends persisted with smoking duration in both current and past smokers. Furthermore, exposure to passive smoke during pregnancy or childhood was associated with an increased risk of psoriasis. The risk of psoriasis among former smokers decreases nearly to that of never smokers 20 years after cessation.

Writing in the article published in The American Journal of Medicine, Hyon K. Choi, MD, DrPH, from Massachusetts General Hospital states, “These findings, along with well-established hazardous health effects of smoking, provide clear incentives for smoking cessation in those at risk for and suffering from psoriasis. Beyond the potential effect on psoriasis, smoking cessation would lead to a better overall clinical outcome in psoriasis patients, who often suffer co-morbidities related to smoking.”